1. Field of the invention
This invention relates to a field effect transister.
2. Related Background Art
We presented a device which can realize low-noise characteristics which are compatible with those of AlGaAs/GaAs-based HEMTs in "Double Pulse-Doped Channel GaAs MESFETs" at 1991 Autumn National Convention of Institute of Electronics and Communication Engineers which was held on Aug. 15, 1991. This MESFET comprises on an S.I. GaAs substrate a 2 .mu.m-thickness p.sup.- GaAs buffer layer, a 50 .ANG.-thickness n.sup.+ GaAs pulse-doped layer having an impurity concentration of 2.times.10.sup.18 /cm.sup.3, a 100 .ANG.-thickness intentionally-undoped n.sup.- GaAs intermediate layer, a 50 .ANG.-thickness n.sup.+ pulse-doped layers of an impurity concentration of 2.times.10.sup.18 /cm.sup.3, an n.sup.- GaAs gap layer (1.times.10.sup.17 /cm.sup.3, 400 .ANG.), and n.sup.+ GaAs contact layers (4.times.10.sup.18 /cm.sup.3, 1000 .ANG.) , which are deposited one on another in the stated order, and has a recess structure in which the cap layer for the channel region is exposed.